This invention relates to apparatus for use with horizontal beam spectrophotometers and, more particularly, to a carrier adapted to carry a microsample holder, the combination of the carrier and holder being used in place of a conventional cuvette support and cuvettes, whereby the spectrophotometer may be used with the carrier and microsample holder in much the same way as the spectrophotometer heretofore has been used with the conventional cuvette support and cuvettes.
Spectrophotometers have long been used as laboratory tools for analyzing or testing liquid samples of, for example, chemical solutions or mixtures, biologic materials, biochemical materials, biochemical reactions or the like. Typically, two types of spectrophotometers generally are available: the vertical beam spectrophotometer, in which the analyzing light beam is transmitted in the vertical direction to a sample disposed in a horizontal plane; and the horizontal beam spectrophotometer in which the analyzing beam is transmitted in the horizontal direction to impinge a sample disposed in a vertical plane. Of these two types of spectrophotometers, the horizontal beam spectrophotometer is more prevalent.
In using a conventional horizontal beam spectrophotometer, samples of the liquid to be analyzed or tested are contained within individual cuvettes which (shown, for example, in FIG. 9 herein), in turn, are carried by a box-like support that is particularly configured for cooperation with the spectrophotometer. As an example, a conventional support is provided with a holding chamber in which four cuvettes are supported in vertical alignment (shown, for example, in FIG. 1 herein). One or both of the larger faces, or walls, of the support is provided with one or more windows through which the horizontal beam passes to a cuvette supported within the holding chamber thereby exposing that cuvette and its contents to the beam. The window may be of a dimension so as to expose all of the individual cuvettes supported within the supporting chamber or, alternatively, a plurality of individual windows, each aligned with a respective cuvette, may be formed in the larger face(s) of the support. Proper separation of the cuvettes within the supporting chamber is achieved by the provision of internal separating walls that may run the entire height of the support or, alternatively, suitable ribs may be formed on the interior walls of the support to separate the cuvettes and provide sufficient support therefor such that the cuvettes remain in proper vertical alignment notwithstanding the manipulation to which the support may be subjected.
When a horizontal beam spectrophotometer is used with the aforementioned conventional support, each of the cuvettes within that support is exposed, in sequence, to the light beam that is transmitted through the window or windows of that support. Automatic indexing means are provided in some spectrophotometers, whereby the support is indexed to place one cuvette and then the next, in sequence, in the path of the horizontal light beam. In less expensive spectrophotometers, the operator must index the support manually to place successive cuvettes in the path of the light beam. As will be described below, it is one salient feature of the present invention to take advantage of the automatic or manual indexing means by which successive liquid samples in the cuvettes are placed in the path of the horizontal light beam.
While conventional horizontal beam spectrophotometers have been readily accepted, one disadvantage attending the use of cuvettes and the aforementioned conventional cuvette support with that spectrophotometer resides in the fact that each cuvette must contain a relatively large sample, on the order of about 200-2000 .mu.l. In some instances, the total quantity of sample that is available is relatively small such that it may not be practical to utilize 200 (or 2000) .mu.l merely for analysis or test purposes. It is, therefore, believed to be desirable to provide apparatus for use with a conventional horizontal beam spectrophotometer which requires the use of far smaller samples, for example, on the order of 5-10 .mu.l, for analysis or test purposes.
Another disadvantage attending the use of cuvettes and the aforementioned cuvette support is the time-consuming requirement of filling each cuvette and inserting it into the support in preparation for analysis by the spectrophotometer. Typically, the conventional support may contain up to four cuvettes, and each cuvette must be inserted individually into that support. If, for example, eight samples are to be analyzed, as may be common, two separate support-loading operations must be carried out, one before each run through the spectrophotometer. In a typical laboratory analysis procedure, scores of samples are analyzed, and the task of loading the support with groups of four cuvettes becomes significantly time-consuming.
Yet another disadvantage associated with the aforementioned cuvettes and conventional cuvette support is the need to cleanse each cuvette prior to filling it with a liquid sample. Since some cuvettes are relatively expensive, it is not practical to provide an endless supply thereof in a typical laboratory. Hence, after several runs utilizing individual cuvettes, those that had been used previously must be cleansed in preparation for re-use. This cleansing operation, coupled with the aforementioned support-loading operation adds significantly to labor costs and results in inefficiencies.
Although one type of improved microsample holder has been proposed for use with conventional vertical beam spectrophotometers, there has been no comparable suggestion heretofore to employ a similar microsample holder for use with horizontal beam spectrophotometers. Neither has there been any suggestion regarding the use of other supports (carriers) for horizontal beam spectrophotometers. It is believed that the particular structure of conventional box-like cuvette supports, normally used with horizontal beam spectrophotometers, has discouraged attempts to design microsample holders for use therewith. Consequently, there has been no incentive to design new supports for such microsample holders for use in horizontal beam spectrophotometers.
The microsample holder that has been proposed for vertical beam spectrophotometers is constructed as a generally rectangular glass plate having one or more rows of circular areas on the order of about 3 mm in diameter, each circular area being adapted to retain a small liquid sample on the order of a 5 .mu.l drop. The surface (or surfaces) of the glass plate surrounding the circular areas is coated with a thin layer of hydrophobic material. In one embodiment of the aforementioned microsample holder, one row of, for example, four circular areas are provided in the plate. In other embodiments, two or more rows of circular areas are provided. The use of such microsample holders is described in, for example, Journal of Bacteriology, Volume 149, No. 1, January 1982, "Specific Antisera and Immunological Procedures for Characterization of Methanogenic Bacteria", by Conway de Macario et al., pages 320-328; Journal of Immunological Methods, Volume 59, 1983, "Quantitative Slide Micro-Immunoenzymatic Assay (Micro-SIA) for Antibodies to Particulate and Nonparticulate Antigens", Conway de Macario et al., pages 39-47; and Journal of Immunological Methods, Volume 68, "Slide Immunoenzymatic Assay for Immunoglobulin Isotype (SIA-Ig)", Conway de Macario et al., 1984, pages 311-318.